Mathematics is what we need. Not sociology. Specifically, we need Set Theory and Group Theory. Whilst this is particularly pertinent if one happens to a RDBMS designer - an occupation in which your muddled and innumerate Pedant-General dabbles - it is perhaps a little less clear why we should ALL need a thorough grounding in this noble pursuit.
Not any more it isn't:
There have been so many times when I have been talking to foreigners - especially our cousins across the pond - when I have needed this diagram. Ah well. At least we do now.
Marching Bands dispatched in the direction of Things of Interest.
Prizes will be awarded for an adaptation of this that successfully includes Gibraltar, Monserrat, the EU, EFTA and NATO.
UPDATE: A very warm welcome to visitors from Harry's Place. I was wondering where all the extra traffic was coming from. (And you may safely ignore my categorisation of HP under the heading "Other Riff Raff and Trouble Makers". At least you are in good company there...)